Wrist and Forearm Postures of Users of Conventional Computer Keyboards

Article excerpt

The aim of this study was to perform a comprehensive investigation to document wrist and forearm postures of users of conventional computer keyboards. We instrumented 90 healthy, experienced clerical workers with electromechanical goniometers to measure wrist and forearm position and range of motion for both upper extremities while typing. For an alphabetic typing task, the left wrist showed significantly greater (p [less than] .01) mean ulnar deviation (15.0[degrees] [plus or minus] 7.7[degrees]) and extension (21.2[degrees] [plus or minus] 8.8[degrees]) than the right wrist (10.1[degrees] [plus or minus] 7.2[degrees] and 17.0[degrees] [plus or minus] 7.4[degrees] for ulnar deviation and extension, respectively). Conversely, the right forearm had greater mean pronation (65.6[degrees] [plus or minus] 8.3[degrees]) than the left forearm (62.2[degrees] [plus or minus] 10.6[degrees]). We noted minimal functional differences in the postures of the wrists and forearms between alphabetic and alphanumeric typing tas ks. Ergonomists should consider the statistically significant and probable practical difference in wrist and forearm posture between the left and right hand in ergonomic interventions in the office and in the design of computer keyboards. Actual or potential applications of this research include guiding the design of new computer keyboards.

INTRODUCTION

The computer keyboard is currently the primary input device for computers and telecommunication. The conventional QWERTY keyboard is a flat keyboard that has a two-dimensional matrix of alphanumeric keys. To rest fingers on the home keys, operators of a conventional keyboard have a tendency to hold their hands and forearms in a biomechanically awkward position. Both forearms are substantially pronated, and both wrists may be deviated in the ulnar direction. In addition, most computer keyboard users hold their wrists in some degree of extension in response to the typical upward slope of the keyboard.

To better understand the mechanical and physiological stresses applied at the wrists and forearms during typing, a thorough understanding of wrist and forearm posture and movement patterns during various typing tasks must be achieved. Prior literature provides some information in that regard. The average position of the wrist in ulnar deviation during typing has been reported to be between 11[degrees] and 25[degrees] (Chen et al., 1994; Honan, Serina, Tal, & Rempel, 1995; Nakaseko, Grandjean, Hunting, & Gierer, 1985; Smith & Cronin, 1993; Sommerich & Marras, 1994; Sommerich, Marras, & Parnianpour, 1996); some authors have reported that the amount of ulnar deviation on the left wrist was a few degrees greater than on the right (Hedge & Powers, 1995; Honan, Jacobson, Tal, & Rempel, 1996). Similarly for wrist extension, the average position of the wrist has been reported as between 13[degrees] and 33[degrees] (Hedge & Powers, 1995; Honan et al., 1995; Honan et al., 1996; Sommerich & Marras, 1994). Limited data exist on forearm pronation, which was reported to range from 69[degrees] to 79[degrees] (Honan et al., 1995; Honan et al., 1996).

After an extensive review of the literature on conventional computer keyboards, we identified the following research limitations: (a) Generally, only a small number of participants have been included in studies that measured physical metrics, such as wrist and forearm posture and range of movement; (b) various methods of measuring wrist motion (including visual observation, videos, and electrogoniometers) may have led to a wide range of values on wrist and forearm position; (c) there is an overall lack of information on pronation/supination of the forearm; (d) authors commonly have only reported mean wrist position, whereas the dynamic aspect of typing has been, for the most part, ignored; and (e) wrist and forearm position was often measured only over a short time (from a few video frames to 60 s). …